The present invention relates to a torque limiter, which transmits a predetermined torque constantly, and stops transmission of torque in case a load more than a predetermined load is applied.
In order to feed a sheet of paper one by one, a paper feeding mechanism for a printer or the like is provided with a rubber-made first roller rotated by a first rotational shaft in a paper feeding direction; a rubber-made second roller rotated by a second rotational shaft in a paper returning direction, outer peripheries of the first roller and the second roller contacting with each other in axial directions; and a torque limiter disposed between the second rotational shaft and the second roller.
Incidentally, the first rotational shaft and the second rotational shaft rotate in the same directions
In the paper feeding mechanism as structured above, in case one sheet of paper is inserted between the first roller and the second roller, since a frictional force between the first roller and the sheet is greater than a set torque of the torque limiter, the second roller is rotated in a direction opposite to the direction of rotation of the first roller, so that the sheet of paper is sent out.
However, in case two sheets of paper are inserted between the first roller and the second roller, since a frictional force between the sheets of paper is smaller than the set torque of the torque limiter, the first roller is rotated in the paper feeding direction to send out one of the sheets, and the second roller is rotated in the paper returning direction to return the other sheet, so that the sheet of paper is sent out one by one.
FIG. 6 is a partly sectional front view of a conventional torque limiter, wherein an upper half of the torque limiter except a shaft is shown in section.
In FIG. 6, numeral 1 designates a shaft which is made of a synthetic resin and is formed into a cylindrical shape. The shaft 1 has a large diameter portion 2, which has an outer diameter slightly smaller than an inner diameter of a magnet 7, described later, and is inserted into the magnet 7. Small diameter portions 3 and 4 are connected to both end sides of the large diameter portion 2 to be inserted into through holes 12 and 15 of a housing 9, described later.
And, the small diameter portion 4 protruded from the housing 9 is provided with an engaging portion 5 with which a pin or the like engages, and a flange 6 having a diameter smaller than the outer diameter of the magnet 7 is provided on an outer periphery of a boundary portion between the large diameter portion 2 and small diameter portion 4.
Numeral 7 is the cylindrical magnet. The magnet 7 has a length in an axial direction (hereinafter simply referred to as a length) approximately the same as the length of the large diameter portion 2, and an inner diameter slightly larger than the outer diameter of the large diameter portion 2.
The magnet 7 is fixed on the outer periphery of the large diameter portion 2 by an adhesive.
Numeral 8 designates a hysteresis member in a cylindrical shape, i.e. magnetic or magnetizable material including a ferromagnetic material. The hysteresis member 8 has a length approximately the same as or longer than the large diameter portion 2, and an inner diameter which allows an inner periphery of the hysteresis member to face the outer periphery of the magnet 7 with a predetermined gap, for example, 0.1 mm, therebetween.
Numeral 9 designates a housing made of a synthetic resin, and the housing 9 is formed of a housing main body 10 and a circular cap 14. The housing main body 10 includes a bottom portion 11 having a circular through hole 12 in the center thereof to which the small diameter portion 3 is inserted, and a cylindrical portion 13 formed around the periphery of the bottom portion 11. The large diameter portion 2 and the magnet 7 abut against the bottom portion 11 through a washer 16, described later. The cap 14 includes a circular through hole 15 at a central portion thereof, through which the small diameter portion 4 is inserted. The cap 14 is fixed to the housing main body 10 by an adhesive such that the cap 14 closes an open end of the housing main body in a condition that the flange 6 abuts against the cap 14.
Incidentally, the housing main body 10 has an inner diameter which allows the hysteresis member 8 to be press-fitted therein by a predetermined force, and an inner size of the housing 9 in an axial direction at a central portion thereof is approximately the same as a length from an end of the large diameter portion 2 at a side of the small diameter portion 3 to an end of the flange 6 at a side of the small diameter portion 4.
Numeral 16 designates the washer which is made of a synthetic resin and shaped in a sheet form. The washer 16 is interposed between the large diameter portion 2 with the magnet 7 and the housing main body 10, so as to set coefficient of friction between the magnet 7 and the housing main body 10 at a predetermined value.
Next, an operation of the conventional torque limiter will be explained.
A rotational shaft omitted in the figure is inserted into the shaft 1 of the torque limiter shown in FIG. 6, and a pin or the like provided at the rotational shaft is engaged with the engaging portion 5 to fix the shaft 1 to the rotational shaft. In this state, when the rotational shaft is rotated in a predetermined direction, by magnetic coupling between the magnet 7 and the hysteresis member 8, the housing 9 is rotated in the same direction as the rotational direction of the rotational shaft.
However, in case a load greater than the torque for integrally rotating the magnet 7 and the hysteresis member 8 is applied to the housing 9, the magnet 7 and the hysteresis member 8 do not transmit the rotational force, so that the housing 9 does not rotate together with the rotational axis.
The respective components forming the torque limiter, i.e. shaft 1, magnet 7, hysteresis member 8, housing main body 10 and cap 14, have tolerances or differences in size, so that a gap between the magnet 7 and the hysteresis member 8 in the assembled condition is different individually. Also, there are differences in sliding characteristics of the sliding portions, such as shaft 1, housing main body 10 and cap 14, and differences also exist in characteristics of the magnet 7 and the hysteresis member 8.
Thus, in case the torque limiter is assembled, the tolerances or differences appear in torque due to various elements.
However, it is impossible to finely adjust the torque to fall within a predetermined range after the torque limiter is assembled. Therefore, it is impossible to improve a yield by lowering defective rate of the torque limiters.
Accordingly, the present invention has been made to solve the aforementioned problems, and an object of the invention is to provide a torque limiter, in which after the torque limiter is assembled, torque can be adjusted to be within a predetermined range to thereby improve a yield.
Another object of the invention is to provide a torque limiter as stated above, in which torque of the torque limiter can be adjusted easily.
A further object of the invention is to provide a torque limiter as stated above, in which the torque limiter can be assembled easily.
Further objects and advantages of the invention will be apparent from the following description of the invention.